Re: [avr-chat] Inline assembler warning: asm operand 2 probably doesn't match constraints

[Joerg Wunsch]

Rick Mann <address@hidden> wrote:

> Ah! I guess here's a case where the compiler isn't smart enough.

No, the problem sits in front of the computer. ;-)

> Theoretically, because the code is inlined, it should be able to
> work out the inverse and then generate the immediate operand for
> andi.

Then you have to constrain it as an immediate value.  If you constrain
it as a register ("r"), the code must use it as a register.  The
compiler cannot analyze your inline assembly code itself; this is just
a "black box" to the compiler.

It's even possible to provide two different implementations, based on
whether it's a compile-time constant or not that is being passed down
to the inline function.  I think it's something like the operator
__constant_p or such (which you have to apply to your mask), please
have a look into the GCC documentation.

-- 
cheers, J"org               .-.-.   --... ...--   -.. .  DL8DTL

http://www.sax.de/~joerg/                        NIC: JW11-RIPE
Never trust an operating system you don't have sources for. ;-)